The invention relates to a method for the manufacture of brushes with a bristle carrier and a bristle facing formed from individual, vertical plastic bristles.
In the present context brushes include all types of floor cleaning implements with a bristle facing, as well as belts, plates, mats, etc. which are faced with bristles. They can in particular be body care or hygienic brushes, such as toothbrushes, massaging brushes, hair brushes, etc., or brushes for applying coating agents, cosmetics, medicaments, etc., or floor mats, brushing belts, polishing belts, etc.
Conventionally with such brushes the bristles are combined into bundles or larger packets and in this form are fixed to the bristle carrier. Previously bundles were fixed mechanically in that a bristle tuft was looped and fixed by means of an anchoring means in the bristle carrier. This fixing procedure is complicated and in some applications, particularly for sanitary brushes, leads to unwelcome secondary phenomena, because the holes which are necessary in the bristle carrier lead to a deposition of dirt and bacteria. In the case of larger diameter bundles or bristle packets, such as are e.g. required in paint brushes, the bundles or packets are fixed in a cement or adhesive bed. With the arrival of plastic bristles other fastening possibilities became available, namely the welding or heat-sealing of the bundles to the carrier or the moulding of the bundle ends into the molten carrier material.
All methods in which the bristle bundles or packets are embedded in a more or less liquid mass and are fixed by the curing thereof, suffer from the decisive disadvantage that the bristles are only inadequately anchored. Thus, after the curing of the mass, the bundles or packets must be combed out to remove loose bristles. Even during use individual bristles, which have an inadequate extraction resistance are released. In certain applications, particularly with paint brushes, coating brushes, etc., this has displeasing consequences, because the separated or released bristles drop into the medium being applied and are difficult to eliminate therefrom without leaving behind traces. In toothbrushes this can have extremely unwelcome consequences, because such detached bristles frequently jam in the interdental space and are difficult to remove.
To the extent that bristle carriers and bristles, as is nowadays usually the case, are made from plastics and joined together by welding, they must be made from the same plastic or material pairs such that they can be integrally welded together to the extent that an adequate joining strength is obtained. This requirement is only fulfilled by a few material pairs and in particular not by those having very different characteristics. However, this is frequently the case with brushes. Thus, the bristle carrier, which normally also forms the brush handle, must generally be rigid and made from an inexpensive plastic, whereas the bristles are made from a high-grade plastic with a comparatively high resistance to wear, good bending capacity and high resistance to alternate flexing. Thus, for bristle carriers use is mainly made of polyolefins, whereas polyamides are used for the bristles. These and other suitable plastic pairs cannot or cannot easily be welded. Much the same applies with respect to the moulding in of the bristles, because here mainly surface adhesive forces must ensure the necessary resistance to extraction, whereas an integral connection only occurs to a limited extent. Therefore the bundles must be melted at their ends to thickened portions in order to produce an additional frictional connection in the carrier.
In addition, brushes are known, in which the bristle facing has, apart from bristle bundles, individual vertical bristles or are made entirely from such individual bristles. Thus, EP 165 546 A1 describes a toothbrush, whose facing partly comprises bristle bundles and partly individual bristles. The individual bristles are arranged in surface-covering manner and, like the bundles, are fixed by welding to the plastic bristle carrier. As has already been intimated, this presupposes specific material pairs and generally required for the carrier the use of a much too expensive plastic so as to adapt to the bristles. Moreover, the bristles obtain their stability and bending capacity and more particularly also their permanent flexing, in that the extruded monofilaments are stretched or drawn and subsequently generally also thermally stabilized, in order to obtain a molecular longitudinal orientation, which is lost as soon as the bristles are exposed to an elevated temperature. Thus, during welding, the fastening-side ends of the bristles are damaged. The bristles lose their bending elasticity and consequently their recovery capacity. The same applies on injecting the bristle bundles into the molten plastic mass of the bristle body and also here the same plastics are recommended for the carrier and the bristles (DE 895 140, 900 809).
In another known toothbrush according to U.S. Pat. No. 4,592,594 the individual bristles are combined into a packet forming the entire bristle facing and are inserted in a frame-like carrier. The bristles are welded together along their circumferential contact faces. Apart from the possible damage to the bristles, in this variant the extraction resistance of the bristles is inadequate, because the contact face with a circular bristle cross-section is substantially only linear and therefore the bristles are only interconnected along four such linear contact faces.
In the case of paint brushes, it is also known (DE 1 050 304 A, U.S. Pat. No. 2,664,316) to melt the entire bristle packet at the fastening-side end and shape same to a plate-like thickening, which serves to maintain the bristle packet in the carrier. It is also known (DE 812 304 B), to mould the bristle packet into the liquid plastic mass of the carrier. More particularly in the case of the first-mentioned construction there occurs the already described damage at the bristle base. However, in the case of paint brushes these methods are particularly unsuitable for use reasons, because the bristles are closely packed and the brush has an inadequate storage space for receiving the application media. Such storage spaces are normally obtained in the case of paint brushes through the use of inserts and the like (DE 92 06 072 U1, DE 30 25 010 A1). These are inserts disposed within the fastening zone and laterally displace the bristles in this area to create chamber-like free spaces immediately adjacent to insert. These free spaces absorb the application medium and release it when pressure is applied to the brush and the bristles bend. These chambers are an essential prerequisite for a uniform application and also for the fact that an adequately large surface can be covered with a single brush stroke. This is particularly important with plastic bristles, because compared with natural bristles they have an inferior retentivity for the application medium. It must also be borne in mind that in all brushes with which media are to be transferred to a surface, the application media have widely differing viscosities. This even applies with toothbrushes with which both paste-like and gel-like dentifrices have to be received and distributed. Consequently, from the use standpoint, brushes only give optimum results in the case of application media having a specific viscosity range, but only operate inadequately with other application media. Therefore, particularly in the case of paint brushes, a large range must be kept in stock in order to create the necessary production prerequisites.
Numerous attempts have been made to fasten bristles in a solitary arrangement to the bristle carrier. Apart from the aforementioned welding, which is unsuitable for material reasons (EP 165 546), it is known (DE 44 10 236) to form bristle monofilaments into loops and in the vicinity of the latter to prefix the monofilaments in rows by warp and weft threads and subsequently to mould with plastic material in the vicinity of the fastening. This method is extremely complicated and costly and always leads to a relatively open structure of the bristle facing. It is also known in connection with larger diameter special bristles (EP 292 693), to weld the bristles to the carrier or to once again loop the bristles and mechanically fix them by means of an anchoring means in the bristle carrier. The disadvantages of both fastening methods have already been explained. It is finally known (GB 2 035 076 A), to inject the bristles in the form of pins and fasten the bristles to the carrier, or to produce the bristles together with the carrier in an injection mould (U.S. Pat. No. 3,583,019, CH 661 851 A5). Here it is not a question of bristles in the normal sense of the term, but of pin-like structures with a relatively large diameter, which necessarily have a completely inadequate retentivity for the application media and which are therefore only suitable for e.g. hairbrushes and the like.
The problems mentioned above are solved by the invention by proposing a method with which the brushes can be manufactured with individual, vertical plastic bristles, in which the bristles have clearly defined and predeterminable spacings, accompanied by the adaptation to the particular coating or application medium and the intended use for the brush.